Plant resistance to pathogens is one of the most important strategies of
disease control. Knowledge of resistance mechanisms, and of how to
exploit them, has made a significant contribution to agricultural
productivity. However, the continuous evolution of new variants of
pathogen, ana additional control problems posed by new crops and
agricultural methods, creates a need for a corresponding increase in our
understanding of resistance and ability to utilize it. The study of
resistance mechanisms also has attractions from a purely academic point
of view. First there is the breadth of the problem, which can be
approached at the genetical, molecular, cellular, whole plant or
population lev ls. Often there is the possibility of productive exchange
of ideas between different disciplines. Then there is the fact that
despite recent advances, many of the mechanisms involved have still to
be fully elucidated. Finally, and compared with workers in other areas
of biology, the student of resistance is twice blessed in having as his
subject the interaction of two or more organisms, with the intriguing
problems of recognition, specificity and co-evolution which this raises.